The present invention relates to a display device, and more particular, to a display device provided on a front surface side thereof with a transparent protective plate. Further, the present invention relates to an appliance provided with such display device.
As display devices mounted on portable appliances such as portable telephones, etc. there are liquid crystal display devices and organic electroluminescence display devices. While these display devices are of a passive drive type and of an active matrix drive type, detailed constructions and operations thereof are well known and so an explanation therefor is omitted.
In the case where these display devices are mounted on portable appliances such as portable telephones, etc., a transparent protective plate is provided on a front surface of a display device in order to prevent an action of a mechanical force applied from outside from disordering or breaking display.
Since a protective plate is different in refractive index from an air, reflection is generated on an interface between the protective plate and an air. That is, with a display device provided with a protective plate, unnecessary interfacial reflection is generated on a front surface and a back surface of the protective plate, so that visibility of the display device is considerably impaired especially in the case where surrounding environment is bright.
As measures to suppress unnecessary reflection generated due to the provision of a protective plate, for example, JP-A-5-11239 discloses a display device, in which an external light reflection preventive layer made of a liquid material having substantially the same refractive index as that of the protective plate is provided between the protective plate and the display device.
In this case, it is possible to suppress reflection on a boundary surface between the protective plate and the external light reflection preventive layer and between the external light reflection preventive layer and the display device.
In the case where an optically transparent layer made of a liquid material is filled as an external light reflection preventive layer between a protective plate and a display device, measures to surround a periphery of the layer with a sealing material becomes necessary in order to prevent leakage of the optically transparent layer from between the protective plate and the display device, thus involving complexity in process and construction.
Therefore, the inventors of the present invention have examined application of a sheet-shaped material as an optically transparent layer instead of a liquid material because the material is favorable in handling and workability. Several problems are caused in application of a sheet-shaped material as an optically transparent layer.
Generally, both a protective plate and a display device are hard, so that in the case where a sheet-shaped material is stuck between hard substances, bubbles are liable to interpose therebetween. In the case where bubbles interpose between an optically transparent layer made of a sheet-shaped material and a protective plate, or between an optically transparent layer and a display device, there is caused a problem that display is degraded in quality since unnecessary reflection is generated in a region, in which bubbles are present.
Also, since a conventional construction includes a clearance composed of an air between a protective plate and a display device, it protects the display device because no force reaches the display device directly even when a mechanical force is applied from outside to deform the protective plate. When a sheet-shaped optically transparent layer is filled between a protective plate and a display device, however, a mechanical force applied to the protective plate from outside becomes liable to be transmitted to the display device and inconvenience attributable thereto is liable to generate.
The invention has been thought of in order to solve such problem in the related art and has its object to realize a display device, in which entrained bubbles are little and display of high quality is obtained.
Also, it is an object of the invention to provide a display device, in which inconvenience is hard to occur even when a mechanical force is applied from outside.
Other tasks and novel features of the invention will be made apparent with reference to descriptions and accompanying drawings of the specification of the present application.